Producing nanostructured Co-Cr-W alloy surface layer by laser cladding and friction stir processing

摘要

The laser cladding Co-Cr-W coating has coarse dendritic and network carbides, which can lead to crack and exfoliation easily, limiting the application of Co-Cr-W coating. In this work, friction stir processing (FSP) was carried out on a laser cladding Co-Cr-W alloy coating to modify its microstructure. FSP transforms the laser clad coarse dendritic grains (grain size: 2-4 μm) into nanograins (grain size: 50-200 nm) and crushes the network carbides into nanoparticles dispersed in Co-base solution. The microstructure and thickness of plastic surface layer are controllable by the condition of FSP. Moreover, a WC_x reinforced Co-Cr-W thin layer was formed because the WC particles of stir tool were squeezed into the Co-Cr-W coating surface layer. More interestingly, when the FSP rotary speed was 1500 rpm, an interlocking bonding between Co-Cr-W coating and steel substrate was formed, which was favorable for the connection with substrate. The surface nanocrystallization significantly strengthened the laser clad Co-Cr-W alloy after FSP.